OK guys, it's time for a new battery. Mine was in the car when I bought it two years ago. It looked like new but I guess it wasn't. It is an AC-Delco group 75 and the "branded" date code can't be read because of a poor stamp job.

The old Delco will only hold 12.3 volts. Charged up it is 12.8 but drops to 12.5 within a day, then settles at 12.3 even with it removed from the car. I thought my starter was getting tired but it's the battery instead.

My question is type of battery. I wanted a AGM but nobody makes one in a group75 size. I also checked on an Oddsey battery but at $289 I don't think I can afford that.An Optma is a little cheaper but the battery shop that sells them advised aganist buying one stating that lately they have had lots of trouble with them.

Will a group 78 fit? I have measured and it seems it might fit but it will be tight. Should I just stick with a Delco Professional Gold? I can get one of those for $130, but a AGM in a 78 size is only $150.

Just my humble opinion, but batteries are relatively cheap. I see no reason to spend a ton of money on one. You should be able to get a decent brand name battery for $100 or less and it wont make your car any slower than the $289 battery. It might not last as long, but at less than half the price, you can replace it every two years and still come out ahead. I have had more than my share of battery troubles, and it seems the "quality" (price) of the battery doesn't make any difference. They all tend to be reliable for 2-3 years.

...I most often put ACDelco's in my vehicles but actually
any good grade battery will do, brands really mean nothing
anymore they all claim the same thing, my only requirement
is that I have a quality alternator installed, I think that is
more important than battery hype.....my $.02

I happen to sell Interstate at my shop and I can say that in the 11 years I've been here, I have seen one battery go bad before the warranty date. It had a bad cell and was replaced free of charge after two years. The MT-75 interstate is a great battery for the vette. I had one in mine before i traded it in. It was in there the nine years I owned it. Tended every year from november to april with no problems. That can be bought for around $100.00.

I have nothing against delcos either. No problems with them in the past. I do recommend you stay away from a walmart battery or advance auto parts silver brand. they are junk. Even Die Hards don't seem to last like they used to. I also don't see a need for an Optima unless you are running amps and speakers. Then that would help a bit.

After purchasing my car in 2005, the original AC battery lasted 1 year. Installed an Optima Red Top. It lasted 1 year.
Tired of spending money on batteries, I made a trip tp Pep Boys and bought a Bosche battery. It's been in the car for 5+ years now, and still performs like new. I have since bought these batteries for my other vehicles and so far have a zero failure rate.

Why do they call it "common sense" when, in fact, it has become so uncommon?

Then installed a Red Top and it did not fail, but was suspect in intermittent electrical issues (never failed to start the car).

Replaced with another Red Top after 2 years... it too was suspect at not delivering full power at all times - also never failed to "start" the car.

I replaced it with a Die Hard Platinum P4 34/78DT CCA 880 RC 135 which EXCEEDS the newer C5 requirements. Installed it last September and have had steady voltage for the longest period so far.

With batteries anymore I think it is luck-of-the-draw. The Die Hard was the most expensive battery I have ever purchased, but so far no complaints. Not sure I really trust any battery over 2-3 years - even though I never had a Red Top fail to start the car.

I happen to sell Interstate at my shop and I can say that in the 11 years I've been here, I have seen one battery go bad before the warranty date. It had a bad cell and was replaced free of charge after two years. The MT-75 interstate is a great battery for the vette. I had one in mine before i traded it in. It was in there the nine years I owned it. Tended every year from november to april with no problems. That can be bought for around $100.00.

I have nothing against delcos either. No problems with them in the past. I do recommend you stay away from a walmart battery or advance auto parts silver brand. they are junk. Even Die Hards don't seem to last like they used to. I also don't see a need for an Optima unless you are running amps and speakers. Then that would help a bit.

Then it must be about time for my WalMart EverStart MAXX 78S battery to die. Purchased 3/16/2010...

A group 78 will fit perfectly. I just installed an Optima Red group 78 which has increased CA and CCA over the 75 AND sufficiant RC; and to me, most importantly, it's sealed.

The C5's unfortunately have a major wiring harness and electronics directly under the battery tray and I heard too many stories of leaking battery acid causing major and costly damage.

My CTEK battery maintainer works perfectly with it too.

I've heard those stories too....
I believe you may find part of the leaking battery issue also involves the use of wrong battery and cable bolt torque. The most important number for the C5's battery is the required minimum 120 rc, even when it is maintained with a battery tender.

I recently won a Optima battery in a buisness card drawing at a ALMS race. Their engineers contacted me to find out which one I wanted. When I told them the one that works in my C5, .....they apologized. The Optima engineers are fully aware of the C5's electrical requirements and minimum 120 rc and still do not manufacture one to address the issues. Anyone will sell you a battery that will "fit" the hole, because they are not aware of the C5's electrical issues.

It is, But I've never EVER had a problem with that. It may be a Vette, but it's still a fairly basic GM system. My wifes Trailblazer SS (LS2) has far more luxuries and electrical demands than my Vette has and it came stock with an AC Delco that only had 90RC. The Red Optima 78s RC is 100. My last battery was a Dynacell group 75 that was only 90RC and it lasted almost 8 years and would last almost 3 weeks without needing a jump. I've never had ANY electrical problems or glitches.

Lots of Vette guys use Optima 78s and 75s (which has lower RC than the 78) and have never had issues.

All "Reserve Capacity" means is the number of minutes a fully charged 12-volt battery at 80 degrees Fahrenheit can provide continous 25 amperes at 10.5 volts (Useful voltage) until the voltage decreases. A battery charger/maintainer keeps your battery charged thus eliminates this concern.

When it was time to replace mine(cracked terminal) I wanted an American made product. There is a fellow near my home that operates a shop that sells only batteries and related items. He sold me a Deka battery and I have had no problems for several years now. If you are interested in originality ,a battery is an easy change.

My 99 C5 had some goofy electrical issues when I bought it. The headlights would come on...by themselves...during the day. There was some other weird crap with the HUD blurring as well.

When I got the A/C fixed my electrical guy said the battery was the wrong type, and didn't have the right specs for the C5. He put an AC Delco in (even though he's an Interstate dealer) it, no issues ever since.

I found it interesting he went with the Delco over the Interstate. He had the car for 10 days, so he had plenty of time to get an Interstate if he thought it was the right battery.

All "Reserve Capacity" means is the number of minutes a fully charged 12-volt battery at 80 degrees Fahrenheit can provide continous 25 amperes at 10.5 volts (Useful voltage) until the voltage decreases. A battery charger/maintainer keeps your battery charged thus eliminates this concern.

With the C5's parasitic draw it is critical to how your electrical system and BCM will function BEFORE you ever turn the key. The C5's unloaded battery minimum is 12.5 volts at 500 CCA per Paul's tech video.

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